Method and apparatus for electrical machining of metal

ABSTRACT

The method of abrasion forming friable material such as carbon blocks to form the electrical discharge machining electrodes therefrom, comprising the steps of moving a master model, having an abrasive surface which is a mirror image of a desired form to be abrasion machined in the friable material, which surface is related in size to the desired form to be machined by an additional movement to be imparted to the master model, toward the friable material with the abrasive surface of the master model and workpiece in engagement while imparting the additional relative motion between the master model and workpiece, which additional relative motion is in all directions in a plane perpendicular to the direction of movement of the master model and workpiece and flushing between the master model and workpiece to prevent buildup of abraded particles of the workpiece on the master model.

()Connor Dec. 10, 1974 METHOD AND APPARATUS FOR ELECTRICAL MACHINING OFMETAL Inventor: Thomas J. OConnor, 100 Morgan Rd, Ann Arbor, Mich. 48106Filed: May 16, 1973 Appl. No.: 360,829

Related U.S. Application Data Continuation-impart of Ser. No, 253,906,May 16, 1972, abandoned, which is a division of Ser. No. 545,652, April27, 1966, Pat, No. 3,663,786.

[52] U.S. Cl. 219/69 M [51 Int. Cl B23k 9/16 [58] Field of Search 219/69M; 204/143 [56] 7 References Cited FOREIGN PATENTS OR APPLICATIONS1,379,623 10/1964 France 219/69 M Primary Examiner-Bruce A. ReynoldsAssistant Examiner-Hugh D. Jaeger Att0rney,'/lger zt, orFirm-Whittemorql-lulbert & Belknap lllllh "HI 57 ABSTRACT The method ofabrasion forming friable material such as carbon blocks to form theelectrical discharge machining electrodes therefrom, comprising thesteps'of moving a master model, having an abrasive surface which is amirror image of a desired form to be abrasion machined in the friablematerial, which surface is related in size to the desired form to bemachined by an additional movement to be imparted to the master model,toward the friable material with the abrasive surface of the mastermodel and workpiece in engagement while imparting the additionalrelative motion between the master model and workpiece, which additionalrelative motion is in all directions in a plane perpendicular to thedirection of movement of the master model and workpiece and flushingbetween the master model and workpiece to prevent buildup of abradedparticles of the workpiece on modelv 8 Claims, 10 Drawing Figures 22 i6s s J I E a 20 I" I; .1 D I E l I0 H j I" a...

the master 1 METHOD AND APPARATUS FOR ELECTRICAL MACHINING OF METAL Thisapplication is a Continuation-in-part of U.S. application Ser. No.253,906, now abandoned, filed May 16, 1972, which application was adivision of application Ser. No. 545,652, filed Apr. 27, 1966, now [1.8.Pat. No. 3,663,786.

The invention relates to electrical discharge machining and refers morespecifically to structure for and a method of producing an electrode orthe like.

In the past, electrodes for electrical discharge machining of metalshave generally been machined from blocks of electrode material, such asgraphite or the like. Themachining of each individual electrodeseparately or even with copy machines, whereby a number of theelectrodes may be machined simultaneously, is a tediousprocess,'wasteful of both man and machine time. In addition theindividual production of electrode on the ram thereof including meansfor moving the electrode in all directions in a plane perpendicular tothe movement of the ram.

Another object is to provide structure as set forth above wherein thetool comprises a pair of slides movable perpendicularly to each otherand eccentric means 7 operable between the pair of slides for relativelymovtrodes by the usual methods produces slight variations I from oneelectrode to another or in the mounting thereof, so that the electrodesare not exactly interchangeable. Thus, a considerable amount of set uptime is required to exactly align an electrode which has beenindividually machined and mounted with a workpiece when changing ofelectrodes is required.

In addition, with prior methods and tools for electrical dischargemachining, it has often been necessary to machine a rough cavity withone or a series of electrodes after which a finish cut is made by aseparate electrode. This is necessary due to wear of the electrode inthe usual electrical discharge machine operation. Again changing of theelectrode between a rough and finish or between two rough or two finishoperations on a workpiece is wasteful of both man and machine time insetup and changing and handling'of the electrodes'even if a quick-changesystem of tooling is used.

It is therefore one of the objects of the present invention to provideimproved structure for producing an electrical discharge machiningelectrode.

Another object is to provide structure for producing an electricaldischargemachining electrode or the like comprising an abrasive mirrorimage electrode from and means for machining a workpiece with the mirrorimage electrode form. t

' Another object is to provide structure as set forth above wherein themeans for machining a workpiece with the mirror image electrode formcomprises a tool for moving the mirror image electrode form universallyin one plane perpendicular to the usual direction of movement of themirror image electrode form.

Another object is to provide an improved method-of producing anelectrode for electrical discharge machining or the like comprisingproducingan abrasive mirror image electrode form and moving themirrorimage electrode form toward a workpiece in a manner to abradethe'desired electrode from electrode material.

Another'object is to provide a method of producing an electricaldischarge machining-electrode as set forth above wherein the manner ofmoving the electrode comprises moving the electrode toward the workpieceand at the same time moving the electrode universally electrcaldischarge machine. I

With particular reference to the Figures of the drawing the slides.Another object is to provide structure as set forth above wherein theeccentric means is adjustable as to eccentricity to determine therelative movement between the slides.

Another object is to provide structure for and a method of producing anelectrode for electrical discharge machining or the like which issimple, economical and efficient.

Other objects and features of theinvention will be come apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings illustrating a preferred embodiment of theinvention, wherein:

FIG. 1 is a perspective view of an electrical discharge machine having atool for producing electrodes or performing other electrical dischargemachining operations in accordance with the invention secured thereto.

FIG. 2 is an enlarged elevational view of the tool illustrated in FIG. 1including a showing of a portion of the ram of the electrical dischargemachine illustrated in FIG. 1.

FIG. 3 is a top view of the tool illustrated in FIG. 2 taken in thedirection of arrow 3 in FIG. 2.

FIG. 4 is a side elevation view of the tool illustrated in FIGS. 2 and 3taken in the direction of arrow 4 in FIG. 3.

FIG. Sis anenlarged partial section view of the tool illustrated inFIGS. 2-4 taken substantially on the line 5-5 in FIG. 3.

FIG. 6 is a perspective view of a tray and a pattern trode form producedthereby.

FIG. 8 is a section view of the mirror image abrasive electrode form ofFIG. 7 secured to a member for mounting on the electrode forming toolillustrated in FIGS..2 through 5. v

FIG. 9 is a partially broken away elevation view of the electricaldischarge machining tool illustrated in FIGS. 2 through 5 having themirror image abrasive electrode electrical secured thereto in positionover a block of electrode material to be formed thereby into, anelectrical discharge machining electrode.

FIG. 10 is an elevation view of an electric discharge machiningelectrode produced in accordance with the method of the inventionsecured to the ram of an ings, one embodiment of the present inventionwill now be disclosed in detail.

In accordance with the invention, the electrical discharge machine tool10 is useful in conjunction with an electrical discharge machine 12 orsimilar structure for producing a finished workpiece with a singleelectrode.

v The finished workpiece may be in accordance with the produced byabrasion with a mirror image abrasive electrode form 14, as illustratedin FIGS. 7 through 9 by the tool 10. i

More specifically, the electrical discharge machining apparatus 12includes a mechanical section 14 having a head mechanism 16 including aram 18 movable vertically to which the electrical discharge machine tool10 is secured by means of a quick-change dovetail arrangement 20 asdisclosed in US. Pat. No. 3,222,494, and an electrical section 22 forproviding an electrical signal between the electrode 24 and a workpiece26 in the usual manner of electrical discharge machining. Servo controlapparatus is provided operable between the electrical section 22 and themechanical section 14 to control movement of the ram 18in accordancewith a gap'maintained between the electrode 24 and-the workpiece 26 inthe usual manner of electrical discharge machines.

Electrical discharge machining apparatus 12 are well known and, forexample, are commercially available from Easco-sparcatron, Inc. of l 10Morgan Road; Ann

Arbor, Mich. They will not be considered in themselves further herein.

The electrical discharge machining tool 10 is shown best in FIGS. 2through in conjunction with a simple electrical discharge machiningelectrode 24. The tool includes the base 28, drive means 30, slidestructure 32 and slide structure 34. Tool 10 is completed by the inder44 of the motor means 30.

Slide structure 32 includes the guides 46 and 48 at the opposite sidesthereof and the slide 50 positioned between the guides 46 and 48. Theguides 46 and'48 are rigidly secured to the base 28 by convenient means,such as bolts 52. The slide 50 is movable between the guides 46 and 48on bearing means 54 and 56. An opening 58 is provided through the slide50 to receive the cam cylinder 60'of the drivemeans 30.

The slide. structure 34 includes the guides62 and 64 rigidly secured tothe slide 50by means of bolts 66 or the like. The slide 68 is movablebetween the guides 62 and 64 on the bearing means 70 and 72 at rightangles to the slide 50. Opening 88 is provided in slide 68 to receivethe cam cylinder 86 of the drive means 30.

The electrode supporting member. 36 is as shown generally rectangularand is secured to the slide 68 by means of bolts 74 or the like.Electrode 24 in the shape of, for example, a recess which it is desiredto machine electricallyin a workpiece 26 is secured to the member 36 byconvenient means, such as bolts 76.

Drive means 30 includes the electric motor 78 which may be energized,such as by a servo mechanism similar to that used to drive the head 18toward the workpiece in the usual electrical discharge machiningapparatus to produce rotation of the output shaft 80 thereof. The drivemeans 30 further includes the cylinder 44 secured to the shaft 80 forrotation therewith which cylinder is concentric with'the shaft 80 and ismounted for rotation in the base 28 by the bearings 42. Cylinder 60 issecured to the shaft 80 and cylinder 44 by means of the pins 82 and 84,as illustrated best in FIG. 5. The drive means is completed by thevcylinder 86 secured in the opening 88 through the slide 68 andeccentrically secured to the cylinder 60 by the bolt 90. Theeccentricity of the cylinder 86 with respect to the cylinder 60 may beadjusted by means of loosening the bolt 90 and rotating the cylinder 86about the bolt 90 and retightening bolt 90. Thus in overall operation ofthe electrical discharge machining tool 10 the usual electricaldischarge machine servo mechanism is used to drive the ram 18 toward aworkpiece whereby the workpiece is formed by the electrode 24 which inthe case of a male electrode is formed slightly undersized. The drivemeans is then caused to rotate whereby the slides 50 and 68 provideuniversal movement of the electrode 24 in a plane perpendicular to thedirection of movement of the ram 18 to finish a workpiece exactly. Thefinishing cut or movement lateral to the ram 18 desired may be adjustedby means of bolt 90 to provide any finishing cut desired. It will bereadily understood that a considerably more sophisticated means foradjustment of the eccentricity between cylinders 60 and 86 may beprovided as desired.

Thus, it will be seen that a very accurately dimensioned workpiece maybe produced by electrical discharge machining without the necessity ofchanging electrodes for a finishing cut through the use of theelectrical discharge machine tool 10 provided in accordance with theinvention.

The electrical discharge machining tool 10 in addition has particularapplication in the production of electrical discharge machiningelectrodes from carbon or graphite blocks or the like, as shown in FIGS.6 through 10, by the method of the invention.

As shown in FIG. 6, to produce a plurality of exactly interchangeablecarbon electrodes for electrical discharge machining a master pattern 98for the electrodes is first machined in the usual manner. The masterpattern 98 is then placed in a molding tay 100 in an inverted position,as shown in FIG. 6. A mixture of abrasive material, such as carborundum,emery or the like, and a plastic binder, such as an epoxy having minimumshrinkage properties, are the poured over the master pattern 98 which isslightly oversized in the case of a male master pattern. Members, suchas small rods, are positiond in the matrix of abrasive material andplastic binder to provide flush openings 102 if desired in the oversizefemale electrode form mirror image 104 produced on setting of theplastic binder, as illustrated in FIG. 7.

After the plastic binder has cured the female electrode form mirrorimage 104 of the male master pattern 98 is removed from the pan 100 andthe pattern 98 and secured to the generally rectangular member 106 bymeans of the bolts 108 in the manner disclosed in applicants US. Pat.Ser. No. 3,497,930, filed of even date herewith.

As shown best in FIG. 9, the member 106 is then secured to the electrodeholding mounting member 36 of the electrical discharge machining tool 10and the tool 10 is advanced toward the carbon block 110 while the drivemeans 30 is actuated to abrade the surface of the electrode form 104 andworkpiece 110. Since the female abrasive electrode form 104 and themaster pattern 98 are slightly oversize an electrode will be formed inthe carbon .block 110 of the exact desired size depending on theeccentricity of the cylinders 60 and 86 of the tool 10.

in addition, since the carbon block 110 is secured to an electrodemounting member 112 having a dovetail locating portin 114 securedthereto and since the tool 110 is provided with similar dovetaillocating structure 38, the electrodes produced with the tool 110 in themanner indicated will be exactly interchangeable so that no time will belost in setting up the electrode 116 produced as indicated abovedirectly on the ram 18 of the electrical discharge machine 12 to performa continuing electrical discharge machining operation as set forth aboveand as illustrated in FIG. 10.

Further, as will be understood by those in the machine tool art,electrical discharge machining electrodes may be formed in accordancewith the method of the invention having the exact dimensions of modelelectrode member by the method of first producing a master die member asset forth above by electrical discharge machining including the steps ofmounting a model electrode member having the dimensions of an electrodeto be formed in parallel relation to a die workpiece member andelectrical discharge machining the die workpiece member with the modelelectrode member to form a cavity in the die workpiece member whilemoving the model electrode member toward the die workpiece member and atthe same time applying an oscillatory rotary motion to one of the modelelectrode member and die workpiece member, as forexample, by means ofthe tool disclosed above, with a predetermined rotary motion amplitudeas set by the eccentricity of the cylinders 60 and '86 of the tool 10.The master die member so formed will have an abrasive surface due to theinherent surface formed by the electrical discharge machining operation.

The electrode members may then be formed with the master die member bymounting an electrode workpiece such as a carborundum block in alignmentwith the master die member, with the master die member secured to thetool 10 and moving the electrode workpiece and master die member towardand into contact with one another while applying rotary oscillatorymotion to one of the electrode workpiece and master die member having anamplitude which is the same as the amplitude used in the production ofthe master die member. In such operation with, for example, a male modelelectrode member, a female master die member which isoversize relativeto the model electrode member is formed so that in later forming theelectrode trode produced from the electrode workpiece is to be used forelectrical discharge machining, it will be necessary to change theamplitude of oscillation of the master die member after a part to beproduced is initially used as a model electrode to form the master diemember so that the electrode formed by the master die member, in thecase of, for example, a male part used as a model electrode member, willbe undersize with respect to the model electrode member by an amountequal to the overcut to be expected in the electrical dischargemachining operation using the electrode formed by the master die member.Thus, when the abrasion machined electrode formed from the electrodeworkpiece is to be used to form parts which are the same size as a partused as a model electrode member in the machining of the master diemember having the abrasive surface, the electrode formed from theelectode workpiece must be of a different size than the model electrodemember by the amount of the overcut which will be produced intheelectrical discharge machining op- While one embodiment of thepresent invention and modifications thereof have been considered indetail, it will be understood that other embodiments and modificationsare contemplated by the inventor. It is the intention to include allembodiments and modifications as are defined by the appended claimswithin the scope of the invention.

What I claim as my invention is:

1. The method comprising the steps of mounting a model electrode memberhaving the dimensions of a workpiece to be formed from a master diemember to be formed from the model electrode member in parallel relationto a die workpiece member, operating upon the die workpiece member withthe model electrode member to form a cavity in the die workpiece'memberand in conjunction with such operation applying oscillatory rotarymotion to one of said model electrode and die workpiece members so as tooscillate the same in its own plane to produce a master die memberhaving a cavity which is oversize relative to said model electrodemember by an amount equal to the total amplitude of the rotary motionand providing an abrasive surface on said master die member.

2. The method'as set forth in claim 1 wherein the operation upon saiddie workpiece member is an electrical discharge machining operation.

3. The method of forming an electrode member for use in an electricaldischarge machining operation comprising mounting an electrode workpiecemember in alignment with a master die member having an abrasive surfaceformed by movement of a model electrode member toward the electrodeworkpiece member while applying an oscillatory rotary motion having apredetermined amplitude to one of the model electrode and die workpiecemember, moving the electrode workpiece member and the master die memberinto contact with one another to force said electrode workpiece memberinto the abrasive surface of said master die member while applyingoscilatory rotary motion to one of the electrode workpiece member andmaster die member whereby through an abrasion operation the electrodeworkpiece member is formed into an elec-' trode member which isundersize relative to the master die member in the case of a maleelectrode member by an amount equal to the total amplitude of theoscillatory rotary motion applied between the master die member andelectrode workpiece member, and controlling the amplitude of theoscillatory rotary motion to be substantially the same as that used toform the master die member.

4. The method as set forth in claim 3 wherein the amplitude of theoscillatory rotary motion between the master die member and electrodeworkpiece is different from the amplitude of the oscillatory rotarymotion used to formthe master die member by the amount of overcutexpected in the use of the electrode workpiece member aft'erit isformed.

5. A method of forming an electrode member for use in an electricaldishcarge machining operation comprising the steps of mounting a modelelectrode member, having the dimensions of the electrode to be formed,in parllel relation to a die workpiece member, operating upon said dieworkpiece member with said model electrodemember to'form a cavity insaid die workpiece member and in conjunction with such operationapplying oscillatory rotary motion to one of said model electrode anddie workpiece members so as to oscillate the same in its own plane toproduce a master die member having a cavity which is oversize relativeto said model electrode member by an amount equal to thetotal amplitudeof said oscillatory rotary motion, providing an abrasive surface on saidmaster die member, mounting an electrode workpiece member in alignmentwith said master die member and moving said members into contact withone another to force said electrode workpiece member into said masterdie member while conjointly applying oscillatory rotary motion to one ofsaid members whereby through an abrasion operation said electrodeworkpiece member is formed into an electrode member which is undersizerelative to said master die member by an amount equal to total amplitudeof said last-mentioned oscillatory rotary motion, and controlling thelatter amplitude so as to be equal to the amplitude of saidfirst-mentioned oscillatory rotary motion whereby the dimensions of theelectrodemember produced by said abrasion operation will be equal to thedimensions of said model electrode member.

6. A method in accordance with claim 5 where the operation on said dieworkpiece member by said model electrode member to form a cavity in thelatter comprises an electrical discharge machining operation.

7. A method in accordance with claim 6 where the step of applyingoscillatory rotary motion to one of said model electrode and dieworkpiece members is carried out simultaneously with said electricaldischarge machining operation.

8. A method in accordance with claim 6 where said abrasive surface isformed on said master die member by means of spark discharge during saidelectrical discharge machining operation.

1. The method comprising the steps of mounting a model electrode memberhaving the dimensions of a workpiece to be formed from a master diemember to be formed from the model electrode member in parallel relationto a die workpiece member, operating upon the die workpiece member withthe model electrode member to form a cavity in the die workpiece memberand in conjunction with such operation applying oscillatory rotarymotion to one of said model electrode and die workpiece members so as tooscillate the same in its own plane to produce a master die memberhaving a cavity which is oversize relative to said model electrodemember by an amouNt equal to the total amplitude of the rotary motionand providing an abrasive surface on said master die member.
 2. Themethod as set forth in claim 1 wherein the operation upon said dieworkpiece member is an electrical discharge machining operation.
 3. Themethod of forming an electrode member for use in an electrical dischargemachining operation comprising mounting an electrode workpiece member inalignment with a master die member having an abrasive surface formed bymovement of a model electrode member toward the electrode workpiecemember while applying an oscillatory rotary motion having apredetermined amplitude to one of the model electrode and die workpiecemember, moving the electrode workpiece member and the master die memberinto contact with one another to force said electrode workpiece memberinto the abrasive surface of said master die member while applyingoscilatory rotary motion to one of the electrode workpiece member andmaster die member whereby through an abrasion operation the electrodeworkpiece member is formed into an electrode member which is undersizerelative to the master die member in the case of a male electrode memberby an amount equal to the total amplitude of the oscillatory rotarymotion applied between the master die member and electrode workpiecemember, and controlling the amplitude of the oscillatory rotary motionto be substantially the same as that used to form the master die member.4. The method as set forth in claim 3 wherein the amplitude of theoscillatory rotary motion between the master die member and electrodeworkpiece is different from the amplitude of the oscillatory rotarymotion used to form the master die member by the amount of overcutexpected in the use of the electrode workpiece member after it isformed.
 5. A method of forming an electrode member for use in anelectrical dishcarge machining operation comprising the steps ofmounting a model electrode member, having the dimensions of theelectrode to be formed, in parllel relation to a die workpiece member,operating upon said die workpiece member with said model electrodemember to form a cavity in said die workpiece member and in conjunctionwith such operation applying oscillatory rotary motion to one of saidmodel electrode and die workpiece members so as to oscillate the same inits own plane to produce a master die member having a cavity which isoversize relative to said model electrode member by an amount equal tothe total amplitude of said oscillatory rotary motion, providing anabrasive surface on said master die member, mounting an electrodeworkpiece member in alignment with said master die member and movingsaid members into contact with one another to force said electrodeworkpiece member into said master die member while conjointly applyingoscillatory rotary motion to one of said members whereby through anabrasion operation said electrode workpiece member is formed into anelectrode member which is undersize relative to said master die memberby an amount equal to total amplitude of said last-mentioned oscillatoryrotary motion, and controlling the latter amplitude so as to be equal tothe amplitude of said first-mentioned oscillatory rotary motion wherebythe dimensions of the electrode member produced by said abrasionoperation will be equal to the dimensions of said model electrodemember.
 6. A method in accordance with claim 5 where the operation onsaid die workpiece member by said model electrode member to form acavity in the latter comprises an electrical discharge machiningoperation.
 7. A method in accordance with claim 6 where the step ofapplying oscillatory rotary motion to one of said model electrode anddie workpiece members is carried out simultaneously with said electricaldischarge machining operation.
 8. A method in accordance with claim 6where said abrasive surface is formed on said master die member by meansof spark discharge during said electrical discharge machining operation.